U.S. patent application number 16/751246 was filed with the patent office on 2020-05-21 for stabilized, high-doped silicon carbide.
The applicant listed for this patent is Cree, Inc.. Invention is credited to Al Burk, Michael O'Loughlin, Adrian Powell.
Application Number | 20200157705 16/751246 |
Document ID | / |
Family ID | 60972415 |
Filed Date | 2020-05-21 |
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United States Patent
Application |
20200157705 |
Kind Code |
A1 |
Powell; Adrian ; et
al. |
May 21, 2020 |
STABILIZED, HIGH-DOPED SILICON CARBIDE
Abstract
Stabilized, high-doped silicon carbide is described. A silicon
carbide crystal is grown on a substrate using chemical vapor
deposition so that the silicon carbide crystal includes a dopant
and the strain compensating component. The strain compensating
component can be an isoelectronic element and/or an element with
the same majority carrier type as the dopant. The silicon carbide
crystal can then be cut into silicon carbide wafers. In some
embodiments, the dopant is n-type and the strain compensating
component is selected from a group comprising germanium, tin,
arsenic, phosphorus, and combinations thereof. In some embodiments,
the strain compensating component comprises germanium and the
dopant is nitrogen.
Inventors: |
Powell; Adrian; (Cary,
NC) ; Burk; Al; (Chapel Hill, NC) ;
O'Loughlin; Michael; (Chapel Hill, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cree, Inc. |
Durham |
NC |
US |
|
|
Family ID: |
60972415 |
Appl. No.: |
16/751246 |
Filed: |
January 24, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15398185 |
Jan 4, 2017 |
10577720 |
|
|
16751246 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/167 20130101;
C30B 23/063 20130101; C30B 33/00 20130101; C30B 23/025 20130101;
H01L 29/1608 20130101; H01L 29/36 20130101; C30B 23/066 20130101;
C30B 23/02 20130101; C30B 29/36 20130101 |
International
Class: |
C30B 29/36 20060101
C30B029/36; C30B 33/00 20060101 C30B033/00; C30B 23/06 20060101
C30B023/06; C30B 23/02 20060101 C30B023/02; H01L 29/36 20060101
H01L029/36; H01L 29/167 20060101 H01L029/167; H01L 29/16 20060101
H01L029/16 |
Claims
1. A method of producing a silicon carbide wafer, comprising:
placing a seed in a growth zone; introducing a nitrogen dopant and
a strain compensating component in the growth zone; positioning a
source material in the growth zone; sublimating a silicon carbide
crystal on the seed; cutting the silicon carbide crystal into a
wafer; wherein the silicon carbide wafer includes the nitrogen
dopant at a nitrogen concentration of from 1.times.10.sup.18
cm.sup.-3 to 1.times.10.sup.21 cm.sup.-3 and the strain
compensating component at a strain compensating component
concentration of from 2.times.10.sup.18 cm.sup.-3 to
2.times.10.sup.20 cm.sup.-3, wherein the strain compensating
component comprises an isoelectronic element and/or an element with
the same majority carrier type as the nitrogen dopant.
2. The method of claim 1 wherein the strain compensating component
is selected from a group comprising germanium, tin, arsenic,
phosphorus, and combinations thereof.
3. The method of claim 1 wherein the strain compensating component
comprises germanium.
4. The method of claim 1 wherein the concentration of the nitrogen
dopant in the silicon carbide wafer is from 1.times.10.sup.18
cm.sup.-3 to 1.8.times.10.sup.20 cm.sup.-3.
5. A silicon carbide wafer having a width where a longest dimension
of the width is from 50 mm to 300 mm; and comprising a strain
compensating component and a n-type dopant of nitrogen at a
concentration from 1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.21
cm.sup.-3, a concentration of the strain compensating component in
the silicon carbide wafer being from 2.times.10.sup.18 cm.sup.-3 to
2.times.10.sup.20 cm.sup.-3, the strain compensating component
including an isoelectronic element and/or an element with the same
majority carrier type as the n-type dopant wherein the strain
compensating component is selected from a group comprising
germanium, tin, arsenic, phosphorus, and combinations thereof.
6. A silicon carbide wafer having a width where a longest dimension
of the width is from 50 mm to 300 mm and a resistivity of less than
0.01 ohm-cm; and comprising nitrogen at a concentration from
1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.21 cm.sup.-3 and a
strain compensating component selected from a group comprising
germanium, tin, arsenic, phosphorus, and combinations thereof,
wherein a concentration of the strain compensating component in the
silicon carbide wafer is from 1% to 180% of the concentration of
the nitrogen.
7. The silicon carbide wafer of claim 6 wherein the concentration
of the strain compensating component is between 3% and 120% of the
concentration of nitrogen.
8. The silicon carbide wafer of claim 6 wherein the nitrogen is in
a concentration from 1.times.10.sup.18 cm.sup.-3 to
1.times.10.sup.20 cm.sup.-3.
9. The silicon carbide wafer of claim 6 wherein the strain
compensating component has a concentration from 2.times.10.sup.17
cm.sup.-3 to 1.times.10.sup.21 cm.sup.-3.
10. The silicon carbide wafer of claim 5 wherein the strain
compensating component has a concentration from 2.times.10.sup.17
cm.sup.-3 to 1.8.times.10.sup.20 cm.sup.-3.
11. A silicon carbide wafer having a width dimension of from 50 mm
to 300 mm comprising a strain compensating component and a n-type
dopant at a concentration of at least 1.times.10.sup.21 cm.sup.-3,
a concentration of the strain compensating component in the silicon
carbide wafer from 1% to 180% of the concentration of the n-type
dopant, the strain compensating component including an
isoelectronic element and/or an element with the same majority
carrier type as the n-type dopant wherein the strain compensating
component is selected from a group comprising germanium, tin,
arsenic, phosphorus, all and combinations thereof.
12. The silicon carbide wafer of claim 11 the strain compensating
component is in a concentration from 2.times.10.sup.17 cm.sup.-3 to
1.times.10.sup.21 cm.sup.-3.
13. The silicon carbide wafer of claim 11 wherein the strain
compensating component comprises germanium and the concentration of
the strain compensating component in the silicon carbide wafer is
from 2.times.10.sup.17 cm.sup.-3 to 1.8.times.10.sup.20
cm.sup.-3.
14. The silicon carbide wafer of claim 11 wherein the n-type dopant
comprises nitrogen.
15. The silicon carbide wafer of claim 11 having a resistivity of
less than 0.01 ohm-cm.
16. The method of claim 11 wherein the concentration of the strain
compensating component is between 3% and 120% of the concentration
of nitrogen.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 15/398,185, filed Jan. 4, 2017 and entitled
"STABILIZED, HIGH-DOPED SILICON CARBIDE," the entire contents of
each of which are incorporated by reference herein for all
purposes.
BACKGROUND
[0002] Silicon carbide (SiC) exhibits many attractive electrical
and thermophysical properties. Silicon carbide is especially useful
due to its physical strength and high resistance to chemical
attack. Silicon carbide also has excellent electronic properties,
including radiation hardness, high breakdown field, a relatively
wide band gap, high saturated electron drift velocity, high
temperature operation, and absorption and emission of high energy
photons in the blue, violet, and ultraviolet regions of the
spectrum. Some of the properties of SiC make it suitable for the
fabrication of high power density solid state devices.
[0003] SiC is often produced by a seeded sublimation growth
process. In a typical silicon carbide growth technique, a substrate
and a source material are both placed inside of a reaction
crucible. A thermal gradient created when the crucible is heated
encourages vapor phase movement of the materials from the source
material to the substrate followed by condensation upon the
substrate and resulting bulk crystal growth.
[0004] It is known that impurities can be introduced as dopants
into SiC and that these dopants can regulate certain properties. If
the SiC is produced in a sublimation growth process as discussed
immediately above, a dopant can be introduced into the chamber in
any of various ways so that the dopant will be present in the SiC
crystal produced from that process. The process is controlled to
provide an appropriate concentration of the dopant for a particular
application.
SUMMARY
[0005] Embodiments of the present invention make use of a strain
compensating component to allow high doping and hence high
conductivity in SiC crystals and wafers. In some embodiments, a
method of producing a SiC crystal includes placing a seed in a
growth zone and positioning a source material in the growth zone,
wherein the source material includes a dopant and the strain
compensating component. The SiC crystal is grown on the seed so
that the SiC crystal includes the dopant and the strain
compensating component. The SiC crystal can then be cut into SiC
wafers. The strain compensating component can be any element that
introduces an opposing strain into the SiC lattice such that the
total net strain is reduced. To achieve this, the concentration of
the strain compensating element can be between 1% and 20% of the
concentration of the dopant. In some embodiments, the concentration
will be between 1% and 180%. In some embodiments, the concentration
will be between 3% and 120%. In some embodiments, the concentration
will be between 5% and 100%. In some embodiments, the concentration
will bet between 20% and 100%.
[0006] In some embodiments of the invention, the strain
compensating component is selected from a group comprising
germanium, tin, arsenic, phosphorus, and combinations thereof. In
some embodiments, a concentration of the strain compensating
component is from 1.times.10.sup.17 cm.sup.-3 to 2.times.10.sup.21
cm.sup.-3. In some embodiments, a concentration of the strain
compensating component is from 2.times.10.sup.17 cm.sup.-3 to
2.times.10.sup.20 cm.sup.-3. In some embodiments, the concentration
of the strain compensating component is from 2.times.10.sup.17
cm.sup.-3 to 1.8.times.10.sup.20 cm.sup.-3. In some embodiments,
the concentration of the strain compensating component is from
2.times.10.sup.17 cm.sup.-3 to 1.times.10.sup.20 cm.sup.-3. In some
embodiments, the concentration of the strain compensating component
is from 1.times.10.sup.18 cm.sup.-3 to 1.8.times.10.sup.20
cm.sup.-3. In some embodiments, the concentration of the strain
compensating component is from 1.times.10.sup.18 cm.sup.-3 to
1.8.times.10.sup.19 cm.sup.-3. In some embodiments, the
concentration of the strain compensating component is from
1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.19 cm.sup.-3. In some
embodiments, the strain compensating component comprises germanium.
In some embodiments, a concentration of germanium in the silicon
carbide crystal is from 1.times.10.sup.17 cm.sup.-3 to
2.times.10.sup.21 cm.sup.-3. In some embodiments where germanium is
used, the concentration of germanium in the SiC crystal and/or
wafer is from 2.times.10.sup.17 cm.sup.-3 to 2.times.10.sup.20
cm.sup.-3. In some embodiments where germanium is used, the
concentration of germanium in the SiC crystal is from
1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.19 cm.sup.-3.
[0007] In some embodiments, the concentration of a dopant in a SiC
crystal and/or wafer is from 1.times.10.sup.18 cm.sup.-3 to
1.times.10.sup.21 cm.sup.-3. In some embodiments, the concentration
of a dopant in a SiC crystal and/or wafer is from 1.times.10.sup.18
cm.sup.-3 to 1.8.times.10.sup.20 cm.sup.-3. In some embodiments,
the concentration of a dopant in a SiC crystal is from
1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.20 cm.sup.-3. In some
embodiments, the concentration of a dopant in a SiC crystal is from
1.times.10.sup.18 cm.sup.-3 to 1.8.times.10.sup.19 cm.sup.-3. In
some embodiments, the concentration of a dopant in a SiC crystal
and/or wafer is from 1.times.10.sup.18 cm.sup.-3 to
1.times.10.sup.20 cm.sup.-3. In some embodiments, the dopant in a
SiC crystal and/or wafer comprises nitrogen. In some embodiments
where the dopant comprises nitrogen, the concentration of nitrogen
in the SiC crystal and/or is from 1.times.10.sup.18 cm.sup.-3 to
1.times.10.sup.21 cm.sup.-3. In some embodiments where the dopant
comprises nitrogen, the concentration of nitrogen in the SiC
crystal and/or is from 1.times.10.sup.18 cm.sup.-3 to
1.8.times.10.sup.20 cm.sup.-3. In some embodiments where the dopant
is nitrogen, the concentration of nitrogen in the SiC crystal
and/or wafer is from 1.times.10.sup.18 cm.sup.-3 to
1.times.10.sup.20 cm.sup.-3. In some embodiments where the dopant
is nitrogen, the concentration of nitrogen in the SiC crystal
and/or wafer is from 1.times.10.sup.18 cm.sup.-3 to
1.times.10.sup.19 cm.sup.-3.
[0008] A SiC wafer according to some embodiments has a dimension of
from 50 mm to 300 mm and comprises a strain compensating component
and a dopant. In some embodiments, the concentration of the strain
compensating component in the SiC wafer is from 1% to 180% of the
concentration of the dopant, and the strain compensating component
includes an isoelectronic element and/or an element with the same
majority carrier type as the dopant. In some embodiments, the
concentration will be between 1% and 20%. In some embodiments, the
concentration will be between 3% and 120%. In some embodiments, the
concentration will be between 5% and 100%. In some embodiments, the
concentration will be between 20% and 100%. In some embodiments,
the strain compensating component is selected from a group
comprising germanium, tin, arsenic, phosphorus, and combinations
thereof, and the dopant is an n-type dopant. In some embodiments,
the dopant comprises nitrogen and the strain compensation component
comprises germanium.
[0009] A SiC wafer according to some embodiments has a dimension of
from 50 mm to 300 mm and a resistivity of less than 0.01 ohm-cm,
wherein the SiC wafer comprises nitrogen in a concentration from
1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.21 cm.sup.-3. In some
embodiments, the concentration of nitrogen is from
1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.20 cm.sup.-3. In some
embodiments, the concentration of nitrogen is from
1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.19 cm.sup.-3. In some
embodiments, the SiC wafer further comprises a strain compensating
component at a concentration 1% to 180% of the concentration of the
nitrogen. In some embodiments, the concentration will be between 1%
and 20%. In some embodiments, the concentration will be between 3%
and 120%. In some embodiments, the concentration will be between 5%
and 100%. In some embodiments, the concentration will be between
20% and 100%. In some embodiments, the strain compensating
component is selected from a group comprising germanium, tin,
arsenic, phosphorus, and combinations thereof. In some embodiments,
the strain compensating component comprises germanium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1A and FIG. 1B illustrate a method of producing a
crystal and a crystal being grown according to example embodiments
of the invention.
[0011] FIG. 2 illustrates an example wafer according to embodiments
of the present invention. The wafer of FIG. 2 also illustrates the
die that would be cut from the wafer to form devices.
[0012] FIG. 3 illustrates another example wafer according to
embodiments of the present invention. The wafer of FIG. 3 also
illustrates the die that would be cut from the wafer to form
devices.
DETAILED DESCRIPTION
[0013] Embodiments of the present invention now will be described
more fully hereinafter with reference to the accompanying drawings,
in which embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
[0014] It will be understood that, although the terms first,
second, etc. may be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another. For example, a first
element could be termed a second element, and, similarly, a second
element could be termed a first element, without departing from the
scope of the present invention. As used herein, the term "and/or"
includes any and all combinations of one or more of the associated
listed items.
[0015] It will be understood that when an element such as a layer,
region or substrate is referred to as being "on" or extending
"onto" another element, it can be directly on or extend directly
onto the other element or intervening elements may also be present.
In contrast, when an element is referred to as being "directly on"
or extending "directly onto" another element, there are no
intervening elements present. It will also be understood that when
an element is referred to as being "connected" or "coupled" to
another element, it can be directly connected or coupled to the
other element or intervening elements may be present. In contrast,
when an element is referred to as being "directly connected" or
"directly coupled" to another element, there are no intervening
elements present.
[0016] Relative terms such as "below" or "above" or "upper" or
"lower" or "horizontal" or "vertical" may be used herein to
describe a relationship of one element, layer or region to another
element, layer or region as illustrated in the figures. It will be
understood that these terms are intended to encompass different
orientations of the device in addition to the orientation depicted
in the figures.
[0017] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" "comprising," "includes" and/or
"including" when used herein, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
[0018] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
invention belongs. It will be further understood that terms used
herein should be interpreted as having a meaning that is consistent
with their meaning in the context of this specification and the
relevant art and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0019] Unless otherwise expressly stated, comparative, quantitative
terms such as "less" and "greater", are intended to encompass the
concept of equality. As an example, "less" can mean not only "less"
in the strictest mathematical sense, but also, "less than or equal
to."
[0020] Highly doped n-type SiC will form stacking faults when a
bias is applied to a device structure. It is believed that this
stacking fault formation and propagation is due to high tensile
stress induced by the presence of the dopant (for example,
nitrogen) in the crystal lattice. Embodiments of the present
invention make use of a strain compensating component to allow high
doping and hence high conductivity in SiC crystals, wafers, and
devices. The strain compensating component induces a compressive
stress in the lattice and counterbalances the tensile stress
induced by the dopant atoms to produce unstressed, and thus,
stabilized material that does not degrade when a bias voltage is
applied. The material will have higher conductivity due to the
higher doping, but without the tendency to form stacking faults.
These characteristics can be advantageous when the material is to
be used for lower voltage devices.
[0021] While various elements might serve in terms of
counterbalancing the stress, an element that is opposite the
majority carrier type relative to the dopant will compromise the
conductivity of the material and reduce or cancel out any gain in
conductivity obtained by using higher dopant concentrations. Thus,
embodiments of the invention use a strain compensating component
that is an isoelectronic element or an element with the same
majority carrier type as the dopant, or a combination of the two.
Germanium, tin, arsenic, and phosphorus are examples. The strain
compensating component can be a single element or a combination of
elements.
[0022] FIG. 1A and FIG. 1B illustrate the process of growing a
crystal according to example embodiments of the invention. In FIG.
1A, crucible 100 contains source material 102. In this example, the
interior of the crucible serves as a growth zone. Source material
102 can include silicon, carbon, SiC, silicon compounds, carbon
compounds, or combinations of any or all of the foregoing. Other
elements such as nitrogen as the dopant and germanium as the strain
compensating component can be included in the source material.
Alternatively one, some, or all of the other elements can be
introduced into the growth zone in ways other than inclusion in the
source material. A seed 104 is fixed to crucible lid 110. The lid
110 with the seed 104 is placed on crucible 100 so that the seed is
suspended in the crucible above the source material, and crucible
100 is heated. As previously discussed, the strain compensating
component should be either isoelectronic or have the same majority
carrier type (n-type or p-type, donor or acceptor) as the dopant.
Other potential strain compensating elements include tin, arsenic,
and phosphorus.
[0023] The source material sublimes and forms SiC on the seed.
Sublimation occurs when the growth zone is heated to a temperature
from 1800 C to 2500 C. While the temperature of the source material
is being raised, the temperature of the growth surface of the seed
is likewise raised to a temperature approaching the temperature of
the source material. Typically, the growth surface of the seed is
heated to a temperature from about 1700 C to about 2400 C. During
the growth process, the crucible is evacuated slowly to reduce
pressure. By maintaining the source material and the growth surface
of the SiC seed at their respective temperatures for a sufficient
time, macroscopic growth of monocrystalline SiC of a desired
polytype will form upon the seed.
[0024] Turning to FIG. 1B, the SiC crystal is grown from source
material in a crucible using a physical vapor transport process.
Crystal growth takes place until the grown crystal 112 reaches its
desired length. The length chosen depends in part on the type of
post-formation processing to be employed. The point where the
growth of crystal 112 should be stopped will also depend on such
parameters as the size and type of crucible and any concentration
of the dopant and strain compensating component in source material
102. This point can be determined in advance through experimental
growths coupled with examination of crystal 112 to determine
concentrations of the impurities.
[0025] Sublimation growth of SiC can be accomplished with various
growth systems, differently sized crucibles, different types of
crucibles of various materials and using varying heating methods.
Specific growth temperatures and pressures can be adapted by one of
skill in the art to accommodate these variables. In the typical
case, where such variables as the type or size of the crucible are
changed, experimental growths may need to be performed as mentioned
above, to settle on the best growth conditions for a specific
system.
[0026] In some embodiments, the SiC crystal is grown so that the
concentration of the strain compensating component in the SiC
crystal is between 1% and 20% of the concentration of the dopant.
In some embodiments, the concentration will be between 1% and 180%.
In some embodiments, the concentration will be between 3% and 120%.
In some embodiments, the concentration will be between 5% and 100%.
In some embodiments, the concentration will bet between 20% and
100%. In some embodiments, a concentration of the strain
compensating component is from 1.times.10.sup.17 cm.sup.-3 to
2.times.10.sup.21 cm.sup.-3. In some embodiments, a concentration
of the strain compensating component is from 2.times.10.sup.17
cm.sup.-3 to 2.times.10.sup.20 cm.sup.-3. In some embodiments, the
concentration of the strain compensating component is from
2.times.10.sup.17 cm.sup.-3 to 1.8.times.10.sup.20 cm.sup.-3. In
some embodiments, the concentration of the strain compensating
component is from 2.times.10.sup.17 cm.sup.-3 to 1.times.10.sup.20
cm.sup.-3. In some embodiments, the concentration of the strain
compensating component is from 1.times.10.sup.18 cm.sup.-3 to
1.8.times.10.sup.20 cm.sup.-3. In some embodiments, the
concentration of the strain compensating component is from
1.times.10.sup.18 cm.sup.-3 to 1.8.times.10.sup.19 cm.sup.-3. In
some embodiments, the concentration of the strain compensating
component is from 1.times.10.sup.18 cm. sup.-3 to 1.times.10.sup.19
cm.sup.-3.
[0027] In some embodiments a SiC crystal has a dimension of from 50
mm to 300 mm and a resistivity of less than 0.01 ohm-cm, wherein
the SiC crystal will include nitrogen as the dopant in a
concentration from 1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.21
cm.sup.-3. In some embodiments, the concentration of nitrogen will
be from 1.times.10.sup.18 cm.sup.-3 to 1.8.times.10.sup.20
cm.sup.-3. In some embodiments, the concentration of nitrogen will
be from 1.times.10.sup.18 cm.sup.-3 to 1.8.times.10.sup.19
cm.sup.-3. The SiC crystal can include any dopant in a
concentration from 1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.21
cm.sup.-3, from 1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.20
cm.sup.-3, from 1.times.10.sup.18 cm.sup.-3 to 1.8.times.10.sup.19
cm.sup.-3, or from 1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.20
cm.sup.-3. The source material in the crucible can be provided in
any of various forms, including but not limited to solid, powder,
or gas. The source material can include silicon, carbon, SiC,
silicon compounds, carbon compounds, or combinations of any or all
of the foregoing. Other elements such as nitrogen as the dopant and
germanium as the strain compensating component can be included in
the source material. Alternatively one, some, or all of the other
elements can be introduced into the growth zone in ways other than
inclusion in the source material. Once the growing crystal of SiC
has reached the desired size, the system is backfilled with an
inert gas to raise the pressure, and the temperature is slowly
reduced to an intermediate temperature, and then more quickly to
room temperature. The intermediate temperature can be from about
150 C to about 500 C. In some embodiments, the intermediate
temperature is from about 175 C to about 225 C.
[0028] FIG. 2 is a schematic illustration of a substantially
circular wafer cut from a crystal made according to an embodiment
of the invention. Wafer 200 can be cut into die, wherein a die 202
can be used to form a device. Further processing, including, but
not limited to, the depositing of additional layers of
semiconductor material prior to cutting the wafer may be necessary
to form working devices. To be put into use, a finished device may
also need to be encapsulated in a package with appropriate contacts
for mounting and/or connection within a circuit.
[0029] FIG. 3 is a schematic illustration of a substantially
rectangular wafer cut from a crystal made according to an
embodiment of the invention. Wafer 300 can again be cut into die,
wherein a die 302 can be used to form a device. Wafers according to
an embodiment of the invention can be of various shapes and sizes.
In the case of a substantially circular wafer, the term
"dimension," as in a dimension being from 50 mm to 300 mm refers to
the diameter. In the case of a rectangular wafer, this dimension
refers to a length of one of the sides, for example, the length in
the longest side. The dimension of a wafer can be from 50 mm to 200
mm, from 50 mm to 300 mm, or from 100 mm to 300 mm, as
examples.
[0030] In example embodiments, SiC material, whether in a crystal,
wafer, or die form factor, includes a dopant in a concentration
from 1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.21 cm.sup.-3. In
some embodiments, the concentration of the dopant is from
1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.20 cm.sup.-3. In some
embodiments, the concentration of the dopant is from
1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.19 cm.sup.-3. In some
embodiments, the SiC crystal and/or wafer further comprises a
strain compensating component at a concentration between 1% and 20%
of the concentration of the dopant. In some embodiments, the
concentration will be between 1% and 180%. In some embodiments, the
concentration will be between 3% and 120%. In some embodiments, the
concentration will be between 5% and 100%. In some embodiments, the
concentration will bet between 20% and 100%. In some embodiments,
the strain compensating component is selected from a group
comprising germanium, tin, arsenic, phosphorus, and combinations
thereof. In some embodiments, the strain compensating component
comprises germanium and the dopant is an n-type dopant such as
nitrogen.
[0031] The material can also be specified in terms of the strain
compensating component, whether germanium or another element. In
some embodiments, the concentration of the strain compensating
component in the SiC crystal and/or wafer is from 1.times.10.sup.17
cm. sup.-3 to 2.times.10.sup.21 cm.sup.-3. In some embodiments, the
concentration of strain compensating component is from
2.times.10.sup.17 cm.sup.-3 to 1.8.times.10.sup.20 cm.sup.-3. In
some embodiments, the concentration of strain compensating
component is from 1.times.10.sup.18 cm.sup.-3 to
1.8.times.10.sup.19 cm.sup.-3. The ratio of the strain compensating
component to the dopant can still be maintained at from 1% to 180%.
In some embodiments, the concentration will be between 1% and 20%.
In some embodiments, the concentration will be between 3% and 120%.
In some embodiments, the concentration will be between 5% and 100%.
In some embodiments, the concentration will bet between 20% and
100%. With any of the combinations of material parameters discussed
herein, crystal material with a resistivity of less than 0.01
ohm-cm can be produced. A crystal and/or wafer with a resistivity
of less than 0.05 ohm-cm can also be produced. Crystals can also
have a resistivity from 0.001 ohm-cm to 0.01 ohm-cm, from 0.005
ohm-cm to 0.01 ohm-cm, or from 0.005 ohm-cm to 0.05 ohm-cm.
[0032] It should be noted that with nitrogen as the dopant and
germanium as the stress compensating component, very high doping
can be achieved because nitrogen solubility is thought to be around
2.6.times.10.sup.20 or where about 0.5% of the atoms in the SiC
crystal are nitrogen. Given the parameters specified herein, the
number of germanium atoms required to compensate the stress caused
by the highest achievable concentration of nitrogen will be well
less than 1% of the number of silicon and carbon atoms, which does
not exceed germanium solubility limits. However, germanium
incorporation may be limited due to stress (expansion of unit cell)
induced by the germanium atom as it incorporates onto a lattice
site. Since the incorporation of nitrogen creates an opposite
stress (shrinking of unit cell) it is expected that the presence of
a high concentration of nitrogen will allow a higher concentration
of germanium to be incorporated into the material. In fact by
balancing the expansion due to germanium, with the contraction
caused by nitrogen, it may be possible to reach significantly
higher levels of germanium incorporation than normally seen in
unbalanced material, thus allowing germanium concentrations of
between 2.times.10.sup.18 and 2.times.10.sup.20 cm.sup.-3 to be
achieved. With germanium the nitrogen solubility limit could be
higher than 1.times.10.sup.21 further reducing SiC resistivity (and
the solubility limit for germanium).
[0033] It should also be noted that the various combinations of
materials, concentrations, SiC growth conditions, and SiC wafer
sizes mentioned herein are not to be interpreted as being exclusive
of other combinations. For example, any concentration mentioned of
a dopant may be able to be combined with any concentration
mentioned of a strain compensating component in any of variously
sized wafers. Portions of the various embodiments discussed can be
combined in different ways. It should also be noted that physical
properties such as resistivity, concentration and concentration
ratios generally apply to wafers cut from a crystal with the given
property and vice versa.
[0034] Although specific embodiments have been illustrated and
described herein, those of ordinary skill in the art appreciate
that any arrangement which is calculated to achieve the same
purpose may be substituted for the specific embodiments shown and
that the invention has other applications in other environments.
This application is intended to cover any adaptations or variations
of the present invention. The following claims are in no way
intended to limit the scope of the invention to the specific
embodiments described herein.
* * * * *